1. Analysis of elements present in frozen sections of growth plate cartilage, using the electron microprobe, have been obtained in 114 regions of the tissue. During the coming year the data will be quantitated, matched to the electron micrographs of the region from which the data were obtained, and interpreted. 2. Quantitative electron probe of a lesion (tibial dyschondroplasia), which arises from incomplete hypertrophy of the growth plate cells, will also be processed in the same manner as the growth plate. 3. Using a preparation of isolated osteoclasts, enriched to 75% by cell volume, we will begin to characterize the cytoskeleton in osteoclasts by using cytoskeletal perturbers (e.g., colchicine, dytochalasin B, cycloheximide), immunocytochemistry and electron microscopy.